The present invention is directed to a method and apparatus for assembling an ultrasonic transducer for use in electrophotographic applications.
In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder or powder suspension referred to as xe2x80x9ctonerxe2x80x9d. Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced.
Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly. In a slightly different arrangement, toner may be transferred to an intermediate surface, prior to retransfer to a final substrate. Transfer of toner from the charge retentive surface to the final substrate is commonly accomplished electrostatically. A developed toner image is held on the charge retentive surface with electrostatic and mechanical forces. A substrate (such as a copy sheet) is brought into intimate contact with the surface, sandwiching the toner thereinbetween.
An electrostatic transfer charging device, such as a corotron, applies a charge to the backside of the sheet, to attract the toner image to the sheet. Unfortunately, the interface between the sheet and the charge retentive surface is not always optimal.
Particularly with non-flat sheets, such as sheets that have already passed through a fixing operation such as heat and/or pressure fusing, or perforated sheets, or sheets that are brought into imperfect contact with the charge retentive surface, the contact between the sheet and the charge retentive surface may be non-uniform, characterized by gaps where contact has failed. There is a tendency for toner not to transfer across these gaps. A copy quality defect results.
That acoustic agitation or vibration of a surface can enhance toner release therefrom is known. Resonators coupled to the charge retentive surface of an electrophotographic device at various stations therein, for the purpose of enhancing the electrostatic function, are known, as in: U.S. Pat. No. 5,210,577 to Nowak; U.S. Pat. No. 5,030,999 to Lindblad et al.; U.S. Pat. No. 5,005,054, to Stokes et al.; U.S. Pat. No. 5,010,369 to Nowak et al.; U.S. Pat. No. 5,025,291 to Nowak et al.; U.S. Pat. No. 5,016,055 to Pietrowski et al.; U.S. Pat. No. 5,081,500 to Snelling; U.S. Pat. No. 5,282,005 to Nowak, et al.; and U.S. Pat. No. 5,329,341 to Nowak, et al.
In the ultrasonic welding horn art, as exemplified by U.S. Pat. No. 4,363,992 to Holze, Jr., where blade-type welding horns are used for applying high frequency energy to surfaces, it is known that the provision of slots through the horn perpendicular to the direction in which the welding horn extends, reduces undesirable mechanical coupling of effects across the contacting horn surface. Accordingly, in such art, the contacting portion of the horn is maintained as a continuous surface, the horn portion is segmented into a plurality of segments, and the horn platform, support and piezoelectric driver elements are maintained as continuous members. For uniformity purposes, it is desirable to segment the horn so that each segment acts individually.
U.S. Pat. No. 4,713,572 to Bokowski, teaches the use of adhesive in adhering a horn to a piezoelectric element. In U.S. patent application Ser. No. 07/620,520, xe2x80x9cEnergy Transmitting Horn Bonded to an Ultrasonic Transducer for Improved Uniformity at the Horn Tipxe2x80x9d, by R. Stokes et al. teaches the use of an epoxy mesh which serves to bond ceramic piezoelectric elements to the surface of the horn as well as provide electrical contact for the A.C. drive voltage to excite the elements. The epoxy mesh behaves as a low pass mechanical filter, attenuating the transfer of energy from the active element to the waveguide. Variations in dimensions of the epoxy mesh, surface finish, and localized pressure during assembly process influence the coupling between the piezoelectric element and the waveguide resulting in nonuniform vibration amplitude across the process width.
An object of the present invention is to produce a simple, relatively inexpensive yet accurate approach to assemble ceramic piezoelectric elements adhesively to a horn, which improves the transducer uniformity of vibration; this has been a goal in the design, and manufacture of such devices.
In accordance with the invention there is provided an apparatus fabricating a resonator including a horn member and a plurality of piezoelectric members which are secured together by an adhesive layer, including a support element for holding said horn securely in place; and a plurality of clamping bars for applying a discrete force to each one of said plurality of piezoelectric members, each one of said plurality of clamping bars is in contact and associated with an individual piezoelectric member from said plurality of piezoelectric elements thereby maintaining a substantially uniform adhesive layer thickness between said horn and each of one said plurality of piezoelectric members. In one embodiment a pneumatic force application system connected to each one of said plurality of clamping bars for supplying said discrete uniform force to each one of said plurality of clamping bars, said pneumatic force application system includes a plurality of air cylinders, each of said plurality of air cylinders having a force applicator connected to each one of said plurality of clamping bars, a common air tank connected in parallel with each of said plurality of air cylinders to provide a common air pressure to each of said plurality of air cylinders. In other embodiments the force application system may be entirely mechanical, such as a series of precalibrated springs, likewise, discretely providing the uniform force.